Method for molding parts

ABSTRACT

A method is disclosed for molding parts. The system comprises a plasticator and press. The plasticator is capable of receiving a plurality of molding materials comprising a predetermined amount of at least thermoplastic polymers and long reinforcing fibers, such as glass fiber. The plasticator is characterized in that it is capable of simultaneously receiving contaminated molding materials and relatively long glass fibers and molding them into a billet wherein the fibers remain substantially undamaged. The billet is subsequently placed in a compression molding press where other materials may be molded or applied to its surface. The method is further characterized in that a single thermal rise is used to plasticate the molding materials. The system employed by the method comprises a plasticator having a screw, a screw drive system, a plurality of heaters and control system to control the pressure and temperature in a barrel of the plasticator so as to create a billet having certain predetermined billet characteristics (such as a desired volume and/or density).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a system and method for molding parts, andmore particularly, a system and method for molding parts fromcontaminated molding materials using a single thermal heat rise.

2. Description of Related Art

In the field of thermoplastic molding, it is common to mold parts usingeither an injection or compression molding process. Due to the size ofthe orifices used in the injection molding equipment, it is oftendifficult to injection mold with reinforcing fibers, such as glassfibers, having a length over one-eighth inch because such fibers are noteasily injected into or conveyed through the injection mold equipment.In addition, it is difficult to use contaminated molding materials suchas those collected in plastics recycling programs unless they have beensubstantially cleaned, processed and put into a usable form and sizeprior to being used in the injection molding equipment. Such cleaningand processing are expensive and can substantially increase the cost ofusing the contaminated materials, thereby making them economicallyimpractical.

Another problem with the thermoplastic processes of the past is that thethermoplastics become degraded and lose, for example, their strengthwhen exposed to multiple heat rises.

In general, there are two basic types of compression molding processeswhich may be used for molding thermoplastics. First, a sheet moldingprocess involves placing a reinforcement, such as a glass mat, betweensandwiching layers of a thermoplastic and heating the materials toproduce a single sheet of material. The single sheet of material is thencut to the desired size and then reheated to molding temperature beforebeing placed in a compression molding press. This process has thedisadvantage of higher cost because of the apparatus required, thematerial handling costs incurred in making the sheet, handling andcutting the sheet, and the like. The material used to make the sheet isalso subject to three thermodynamic cycles, a first cycle when thethermoplastic sheet is formed, a second cycle when the thermoplasticsheets and glass mat are molded together, and a third cycle when theresulting sheet is heated to molten temperature prior to molding thepart.

The second form of thermoplastic compression is bulk molding compoundsby producing a billet of molten material that is placed into acompression molding press which molds the molten material into a part.Effectively placing and distributing long reinforcing fibers in thebillet has heretofore required complex machinery. For example, U.S. Pat.No. 5,165,941 issued to Ronald C. Hawley on Nov. 24, 1992, discloses anextruder apparatus and process for compounding thermoplastic resin andfibers. The Hawley extruder includes an apparatus for compoundingthermoplastic resin and reinforcing fibers incorporating a resinextruder in which thermoplastic resin pellets are melted in a second,compounding, extruder in which the molten thermoplastic resin is mixedin intimate contact with long reinforcing fibers. The meltedthermoplastic resin is not fed into the device with the fibers, butrather is introduced into the compounding extruder at a point downstreamof the inlet point for reinforcing fibers, so that the fibers aremechanically worked and heated before coming into contact with heated,molten thermoplastic resins.

The Hawley device generally suffers from complexity that raises theinvestment and maintenance costs.

The compression molding of products using polymeric material and glassfibers has traditionally produced a material referred to as fiber glassreinforced plastic. This material exhibits characteristics better thanthe unreinforced plastics, but does not exhibit strength, elasticity orimpact resistance comparable to thermoplastic materials which arespecifically designed to exhibit these characteristics. Most fiberglassreinforced plastic currently in the market is thermoset and isessentially a solidified mixture of fiber glass and plastic withoutbenefit of chemical bonding or specific methods of enhancing polymerentrapment of the glass fibers because the glass fibers are merelyimmobilized in the resin in which it is embodied. In addition, thermosetmaterials are generally not recyclable other than as filler materials,while thermoplastic materials can be remelted and remolded.

What is needed, therefore, is an apparatus and method for moldingthermoplastic parts which is simple and economical and which preservesthe length of the reinforcing fibers, evenly distributes the reinforcingfibers or any other filler materials while maintaining flexibility ofthe material type in products fabricated, is capable of compatibilizingvarious contaminated thermoplastics to allow use of post consumerrecycled material, and which provides a compounding and fabricationenvironment which promotes chemical bonding and molecular orientation toenhance the characteristics of the molded part.

SUMMARY OF THE INVENTION

It is therefore a primary object of this invention to provide a methodand apparatus which facilitates overcoming one or more of theaforementioned problems.

In one aspect of the invention, this invention comprises: a plasticatorfor creating a billet of moldable material including a feeder forreceiving a plurality of molding materials comprising a predeterminedamount of a polyester, other carbocylics and reinforcing fibers, and asuspender coupled to said feeder for receiving the molding materials,for creating a molten suspension of said molding materials withoutdamaging a substantial number of the reinforcing fibers, and also forcreating the billet.

In another aspect of the invention, this invention comprises: a methodfor creating a billet for molding a part comprising the steps of (a)loading a plasticator with molding materials, the molding materialscomprising a polyester, other carbocylics and reinforcing fibers; (b)heating the molding materials to a predetermined temperature; (c)blending the molding materials in order to create a molten suspensionwherein a majority of the reinforcing fibers remain generally undamaged;and (d) extruding the molten suspension in order to form a billet havingpreselected billet characteristics.

In yet another aspect, this invention comprises: a plasticator forcreating a billet from a plurality of molding materials, the plasticatorcomprising plasticating means for receiving the molding materials andfor creating a molten suspension of the molding materials; and controlmeans associated with the plasticating means for controlling thesuspension characteristics applied to the molding materials in order toplasticate the plurality of molding materials into a billet havingpredetermined billet characteristics.

In still another aspect, this invention comprises: a system for moldinga part comprising a plasticator for creating a billet from a pluralityof molding materials, the plasticator comprising plasticating means forreceiving the molding materials and for creating a molten suspension ofthe molding materials, control means associated with the plasticatingmeans for controlling the suspension characteristics applied to themolding materials in order to plasticate said plurality of moldingmaterials into a billet having predetermined billet characteristics; anda press having a mold for receiving the billet and for molding thebillet into the part.

In yet another aspect, this invention comprises: a plasticating processcomprising the steps of loading a plasticator with a plurality ofmolding materials, creating a mixture with the plurality of moldingmaterials in the plasticator, and plasticating the mixture of theplurality of molding materials at a controlled temperature and pressurein order to create a billet having predetermined billet characteristics.

In a still further aspect, the invention comprises: a screw for use in aplasticator having a barrel, said screw comprising a root and aplurality of threads configured to permit a polyester, other carbocylicsand a plurality of reinforcing fibers to be mixed to provide a billethaving predetermined billet characteristics without damaging asubstantial number of the reinforcing fibers.

It is an object of this invention to provide a system and method forusing long reinforcing fibers that can be loaded simultaneously alongwith the thermoplastics being used.

Another object is to facilitate providing a system and method which issimple and economical and which provides a process that generallypreserves the length of the reinforcing fibers through the plasticatingand molding process.

Another object of this invention is to provide a method and apparatuswhich evenly distributes any filler materials, such as reinforcingfibers, which are used in the apparatus and method.

Still another object of the invention is to provide a method andapparatus which facilitates using contaminated molding materials whichhave heretofore been undesirable for use because of their contaminationor because they are expensive to clean sufficiently for use.

Still another object of this invention is to provide a method andapparatus which facilitates or enhances chemical bonding and molecularorientation of the polymer molding materials being used.

These objects and others will be more apparent when the followingdescription is read in conjunction with the claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a system according to one embodiment of theinvention, comprising a plasticator and a press;

FIG. 2 is a fragmentary view of the plasticator shown in FIG. 1;

FIG. 3 is a fragmentary sectional view showing a screw positioned in abarrel which may be used in the plasticator shown in FIGS. 1 and 2;

FIG. 4 is a view similar to FIG. 3 showing a screw having a plurality ofpitch diameters or distances;

FIG. 5 is a sectional view showing the beginning of the plasticatingprocess;

FIG. 6 is a sectional view similar to FIG. 5 showing the screwwithdrawing from a passageway in the barrel;

FIG. 7 is another view showing the screw withdrawing further from thepassageway in the barrel;

FIG. 8 is a view similar to FIG. 7 showing a knife blade in an openposition;

FIG. 9 is a view showing the screw acting as a plunger and forcing themixed suspension of molding materials out of an extrusion end of thebarrel;

FIG. 10 is a view similar to FIG. 9 showing the knife in the closedposition, thereby severing the mixed suspension of molding materials toprovide a billet;

FIG. 11 is a top view showing a screw drive system in a home position;

FIG. 12 is a view similar to FIG. 11 showing the screw drive systemwithdrawing the screw from the barrel;

FIG. 13 is another view showing the screw drive system after it haswithdrawn the screw further from the barrel;

FIG. 14 is an end view of the plasticator showing a knife assembly usedin the plasticator;

FIG. 15 is a view similar to FIG. 14 showing a knife activated to afully open position; and

FIG. 16a and 16b, taken together, are schematic diagrams showing aprocess according to an embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to FIG. 1, a system 10 for molding a part is shown. Thesystem 10 comprises a plasticator 12 for receiving a plurality ofmolding materials 14 and also for plasticating the molding materials 14into a billet 16. The system 10 also comprises a press 18 associatedwith the plasticator 12 for receiving the billet 16 and for molding thebillet 16 into the part (not shown) defined by a mold 20.

The plasticator 12 comprises a base 22 which supports the variouscomponents of the plasticator 12. The base 22 has a support column 24which supports a stationery block 26. The plasticator 12 comprises asuspender or barrel 28 having a feeding end 28a mounted to thestationery block 26. The plasticator 12 also comprises a screw 30 (FIG.3) which is rotatable and axially mounted in barrel 28 as describedbelow.

The system 10 comprises a controller/microprocessor 32 for controllingthe operation of the plasticator 12 and press 18. The controller 32includes an operator control box 34 for interfacing with controller 32.A suitable controller is the Model Slick 150 manufactured by AllenBradley of Fairfield, N.J., but it should be understood that anysuitable controller which is capable of controlling the operation of thesystem may be used.

As best illustrated in FIG. 1, the plasticator 12 further comprisesfeeding means or a feed hopper 36 having an opening 38 for receiving themolding materials 14. The feed hopper opening 38 may be directlyconnected to a supply system (not shown) for moving materials from astorage or drying area (not shown) to the system 10. The feed hopper 36may include an agitator 40 (FIG. 2) for facilitating agitating andmixing the molding materials 14. The agitator 40 is coupled to a drivemotor 42 which in turn is coupled to a control box 44 which controls thespeed and operation of the drive motor 42. In one embodiment, thecontrol box 44 is coupled to controller 32, thereby permitting thecontroller 32 to control the operation of the drive motor 42. The drivemotor is an electric drive motor, but it could be any suitable type ofmotor for driving the agitator, such as a hydraulic or pneumatic motor.

The feed hopper 36 has an end 36a coupled to stationery block 26 so thatthe molding materials 14 may be fed into a feeding opening 46 (FIG. 3)in the feeding end 28a of barrel 28.

The feeding means or feed hopper 36 may comprise a preheater 48 (FIG. 1)which is coupled to controller 32 for preheating the molding materials14 to a preheated temperature before the molding materials 14 areintroduced into the feeding opening 46 in barrel 28. In the embodimentbeing described, the preheater 48 may preheat the molding materials 14in feed hopper 36 to between 100 and 300 degrees Fahrenheit, dependingon the molding materials 14 selected and used. Although not shown, thefeed hopper 36 may be insulated to facilitate maintaining thetemperature in the feed hopper at the preheated temperature.

The suspender or barrel 28 has a feeding end 28a and also an extrudingend 28b from which billet 16 is extruded. In one embodiment, the barrel28 is approximately four feet long and has an outside diameter ofapproximately eight inches and an inside diameter of approximately fourinches. The barrel 28 is manufactured from hardened steel and weighsapproximately 300 pounds. The barrel may have a die 50 located at theextruding end 28b. The function of the die 50 is to cause the billet 16to be extruded into a predetermined shape or diameter. For example, thebillet 16 may be extruded so that its cross-sectional diameter isapproximately 2.0 inches.

As illustrated in FIGS. 3-10, the barrel 28 comprises a feeding portion54, a blending portion 56 and an extruding portion 58. The plasticator12 also comprises the screw 30 which is rotatively and axially mountedin a passageway 52 defined by barrel 28. Notice that screw 30 comprisesa feeding end 30a and an extruding end 30b. The screw 30 furthercomprises a feeding section 60 associated with the feeding end 30a, ablending section 62, and an extruding section 64 associated withextruding end 28b. The feeding section 60, blending section 62 andextruding section 64 of screw 30 become generally associated with thefeeding portion 54, blending portion 56 and extruding portion 58,respectively, of barrel 28 when the screw 30 is located in a homeposition generally shown in FIGS. 3-5.

The feeding section 60 comprises a first plurality of threads 66. Theblending section 62 comprises a second plurality of threads 68, and theextruding section 64 comprises a third plurality of threads 70.

As illustrated in FIG. 3, the first plurality of threads 66 have adepth, identified by double arrow 72, which is generally greater thanthe depth, identified by double arrow 74, of the second plurality ofthreads 68 associated with the blending section 62 of screw 30. Thefirst and second plurality of threads 66 and 68 may have a depth whichis greater than the depth 76 of the third plurality of threads 70associated with extruding section 64. It is to be noted that screw 30comprises a shaft or a root or core 30d about which the first, secondand third plurality of threads 66, 68 and 70 are located. As bestillustrated in FIGS. 2 and 3, the core 30d may be generally tapered toprovide a screw depth that generally decreases from the feeding end 30ato the extruding end 30b. This facilitates ensuring that the depth 72 ofthe first plurality of threads 66 is generally greater than the depth 74of the third plurality of threads 70.

Another embodiment of the screw 30 is shown in FIG. 4. In thisembodiment, the second plurality of threads 68 are provided with agreater number of threads (i.e., a smaller pitch or distance betweenthreads) than the first plurality of threads 66. The embodiments shownin FIGS. 3 and 4 facilitate controlling the mixture and suspension timeof the molding materials 14 and, further, mixing the molding materials14 with a predetermined pressure and shear, without significantlydamaging the molding materials 14 as the screw 30 rotates.

In one embodiment the screw 30 is approximately 100 inches long and hasa core 30d diameter of approximately 3.7 inches. The screw 30 is aleft-hand screw, and the depths 72,74 and 76 are 0.8 inch, 0.6 inch, and0.75 inch, respectively. The blending section 62 of screw 30 has about30% more turns in FIG. 4 when compared to the feeding section 60.

The plasticator 12 also comprises means for driving screw 30 or a screwdrive system 75 for rotatably and axially driving the screw 30 in apassageway 52 (FIG. 3) of barrel 28. The screw drive system 75 iscapable of controlling the rotational and axial movement of screw 30 inthe barrel 28 in order to facilitate mixing the molding materials 14into a molten suspension and ultimately, into billet 16 having certainpredetermined characteristics. When the mixed molten suspension achievesthe predetermined characteristics, such as a predetermined volume,density, viscosity, or size as indicated by predetermined temperatureand pressure, then screw 30 is allowed to withdraw in the direction ofarrow 77 in FIG. 3 to permit the suspension to be formed into the billet16 at a storage or extruding area 124 of barrel 28. As described below,the screw drive system 75 is also capable of controlling the rotationalspeed of screw 30 and the axial movement of screw 30 until the desiredpredetermined characteristics are achieved.

The screw drive system 75 (FIG. 2) comprises means coupled to screw 30for rotatably driving screw 30 and also for axially driving screw 30into and out of passageway 52 (FIG. 2) in barrel 28. The means comprisesa slidable block 78 which is slidably mounted on a pair of stationarycolumn supports 80 and 82, each having an end (such as 92a) secured tostationary block 26. The means also comprises suitable bearings (notshown) located in slidable block 78 for facilitating the axial movementof slidable block 78 in the direction of double arrow 84 in FIG. 2.

The screw drive system 75 also comprises a block driver 86 for slidablydriving the slidable block 78 in the direction of double arrow 84. Inthe embodiment being described, the block driver 86 comprises a pair ofpush/pull hydraulic cylinders 88 and 90 (FIGS. 11-13). The screw drivesystem 75 also comprises a drive motor 92 which is coupled to screw 30and which rotatably drives screw 30 in either a clockwise orcounterclockwise direction as desired. In the embodiment beingdescribed, the drive motor 92 is a hydraulic motor which is capable ofrotating screw 30 at approximately 0 to 100 RPM's.

The screw drive system 74 may comprise first sensing means or sensor 94for sensing the RPM's of drive motor 92. First sensing means 94 may alsoinclude a torque sensor (not shown) which is coupled to controller 32and which monitors or senses the torque of screw 30 as it produces thebillet 16.

The plasticator 12 comprises power means or a power system 96 forenergizing drive motor 92 and block driver 86. In the embodiment beingdescribed, the power system 96 comprises an electric motor 98 whichdrives a hydraulic pump 100. The hydraulic pump 100 pumps oil from areservoir 102 through filter 104 into control means or control block106. The control block 106 comprises pressure valves 108, 110, 112, 114and 116 which control the delivery of fluid to cylinders 88, 90, drivemotor 92 and to a knife driver 118 as described below. The pressurevalves 108, 110, 112, 114 and 116 are coupled to controller 32 which iscapable of controlling their operation as described below.

The power system 96 may comprise a plurality of variable pressureregulators, such as regulator 117, which may be positioned between thedrive motor 92, cylinders 88 and 90 and their respective pressure valvesin order to facilitate controlling the hydraulic pressure deliveredthereto. For example, the pressure regulator associated with thecylinders 88 and 90 can be adjusted so that the pressure delivered tocylinders 88 and 90 can be varied. One suitable pressure regulator isthe Vickers regulator, manufactured by Vickers of Troy, Mich. Thispermits an operator to vary the amount of pressure at which the slidableblock 78 is biased towards the stationary block 26.

As the screw drive system 75 drives and forces molding materials 14 intoa storage area 124 (FIG. 3) associated with the extruding portion 58 ofbarrel 28, the pressure in the barrel 28 begins to build. Such pressureincreases as more of the molten suspension of molding materials 14 areforced and driven into the storage area 124. When such pressure reachesor exceeds the predetermined pressure being delivered to cylinders 88and 90, the pressure causes screw 30 to withdraw from passageway 52 asshown in FIGS. 3-5. Consequently, by controlling the pressure deliveredto cylinders 88 and 90, the density, volume and viscosity of the moltensuspension and the billet 16 can be accurately controlled. By adjustingthe pressure delivered to cylinders 88 and 90, the viscosity, volume anddensity of the molten suspension and billet 16 can be made to conform tothe desired material characteristics and controlled. Although not shown,other types of regulators may be used. For example, electronic orpneumatic regulators may be provided which is coupled to controller 32for automatically adjusting the pressure delivered to cylinders 88 and90 and drive motor 92.

As best illustrated in FIG. 2, the system 10 also comprises sensingmeans or a second sensor for sensing the pressure in the power system96. In the embodiment being described, the sensing means comprises apressure gauge 126 for measuring the pressure being delivered by thehydraulic pump 100. In addition, sensing means also comprise pressuregauge 128 for sensing the pressure being delivered to cylinders 88 and90. Although not shown, it should be appreciated that sensing meanscould comprise any suitable hydraulic, electronic or other suitablemeans which are capable of sensing the pressure being delivered bycontrol block 106 to drive motor 92, knife driver 118, and cylinders 88and 90.

The plasticator 10 also comprises an adjustable distance sensor 130which senses the travel distance of screw 30 as it withdraws from thepassageway 52 of barrel 28. When the actual travel distance reaches apreset distance, the distance sensor 130 generates a distance signalwhich is received by controller 32. Upon receipt of the distance signal,controller 32 energizes pressure valves 108, 110, 114 and 116 to shutthe fluid pressure being delivered to cylinders 88, 90 and drive motor92. As described later herein, controller 32 may then energize pressurevalve 112 to deliver fluid to knife driver 118 in order to drive knifeblade 120 into the open position shown in FIGS. 9 and 15. Controller 32may then energize control block 106 and pressure valve 108 to actuatehydraulic cylinders to pull or slidably drive slidable block 78 towardsstationary block 26 which causes the molten suspension to be extrudedout of extruding opening 132 (FIG. 9) associated with the extruding end28b of barrel 28. Controller 32 may then energize knife driver 118 toforce knife blade back into the closed position shown in FIGS. 10 and14, thereby severing the molten suspension to provide billet 16.

It should be noted that the distance sensor 134 comprises a bracket 136which has an end 136a secured to slidable block 78. The distance sensor134 also has a switch 138 secured to the bracket 136. A plurality ofcontact switches are slidably mounted on a panel 148 (FIG. 1) which issecured to stationary block 26. The panel 148 has distance indiciathereon, and the contact switches 140 can be slidably adjusted on thepanel 148 to generally correspond to the volume of the billet 16 to beextruded from barrel 28. Thus, as slidable block 78 moves in thedirection of arrow 122 and thereby causes screw 30 to withdraw frompassageway 52, contact switch 140, for example, contacts switch 138,thereby generating the distance signal which is received by controller32. Although not shown, it should be appreciated that the distancesensor could be any suitable means for measuring the size, includingvolume, of the billet 16 which is being created. For example, othersuitable electrical, optical, hydraulic, pneumatic, or other types ofsensors may be employed for measuring the distance the screw 30 andblock 78 travels.

The system 10 comprises heating means or a heater for plasticating themolding material 14 using a single thermal cycle from introduction ofmaterials 14 to molding a part or product from billet 16. As illustratedin FIGS. 1 and 2, the plasticator 10 comprises heating means or a heatersystem, 150, in the embodiment being described, which comprises threesets of resistance or heating bands 152, 154 and 156. The heating bands152, 154 and 156 on the barrel 28 are associated with the feedingportion 54, blending portion 56 and extruding portion 58, respectively,as illustrated in FIGS. 3-5. The heating bands 152 heat the feedingportion 54 to a first predetermined temperature. Likewise, the heatingbands 154 heat the blending portion 56 to a second predeterminedtemperature, and the heating bands 156 heat the extruding portion 58 toa third predetermined temperature.

The heating bands 152, 154 and 156 are coupled to heater controller 158which is capable of energizing the heating bands 152, 154 and 156 toheat barrel 28 the first, second and third predetermined temperatures,respectively. The heater controller 58 comprises a third sensing meansor a third sensor for sensing the actual temperature of the feedingportion 54, blending portion 56 and extruding portion 58, respectively,of barrel 28. The heater controller 158 also comprises display means ora display consisting of displays 160 (FIG. 2) for displaying the actualtemperature sensed by heater controller 158. The heater controller 158is coupled to controller 32 which may also control the operation ofheater 150 in heating bands 152, 154 and 156. In the embodiment beingdescribed, the first predetermined temperature associated with thefeeding portion 54 ranges from 300 to 500 degrees Fahrenheit, dependingon the molding materials 14 being used. Likewise, the second and thirdpredetermined temperatures may also range from 300 to 500 degreesFahrenheit. Although these ranges are shown, they are not meant to belimiting and other ranges may be appropriate, depending upon the moldingmaterials 14 and desired or predetermined billet characteristics beingused.

Although not shown, the barrel 28 and heating bands 152, 154 and 156 maybe insulated to facilitate minimizing heat loss in barrel 28.

The heating means may also include the preheater 48, a knife bladeheater, and a mold heater 182, to facilitate providing one thermal rise.In the embodiment being described, the mold heater 182 may compriseModel Nos. S-8412 or 3412 Sterl-Tronic Temperature Control manufacturedby Sterl Co. of Milwaukee, Wis. Furthermore, a screw heater (not shown)may also be provided to heat screw 30 to further facilitate heating themolding materials 14 in barrel 28.

The plasticator 12 also comprises a separator or knife assembly 162(FIGS. 14 and 15) for separating the molding materials 14 to provide thebillet 16. The knife assembly 162 is associated with the extruding ends28b of barrel 28 and comprises a pair of L-shaped mounting brackets 164and 166 which define a channel 168. The knife assembly 162 alsocomprises the knife blade or knife 120 which is slidably mounted inchannel 168. The knife blade 120 is coupled to knife driver 118 which iscapable of driving the knife from the closed position in FIG. 14 to theopen position in FIG. 15 and vice versa. The knife driver 118 comprisesa push/pull type cylinder in the embodiment being described which iscoupled to pressure valve 112 which in turn is coupled to controller 32as mentioned previously herein.

The knife assembly 162 comprises a pair of switches 170 and 172 whichcooperate with a trigger bar 174 located on knife blade 120. The trigger174 triggers switch 170 to generate a closed signal when the knife 120is in the closed position. Likewise, the trigger 174 causes switch 172to generate an open signal when the knife 120 is in the open position.The switches 170 and 172 are coupled to controller 32 which receive theopen and closed signals.

It should be appreciated that due to the proximal location of the knife120 to the extruding end 28b of barrel 28 and die 50, the knife 120becomes heated to approximately the same temperature as the extrudingportion 58 of barrel 28. Note also that when the knife 120 is in theclosed position, it seals the passageway 52 (FIGS. 3 and 4) of barrel 28so that the molded suspension of molding materials 14 can be forcedagainst the barrel side 120a (FIG. 3) of knife 120. Although not shown,the knife 120 may also be provided with the knife heater mentioned abovewhich would be coupled to controller 32 to facilitate heating the knife120 to a predetermined knife blade temperature which would generallycorrespond to the third predetermined temperature.

The system 10 comprises press 18 (FIG. 1) which comprises a press driver176 which is coupled to a press controller 178 which may also be coupledto controller 32. The press controller 178 may energize press driver 176to drive platform 180 from an open or non-molding position shown in FIG.1 to a closed or molding position (not shown). As illustrated in FIG. 1,platform 180 may have a mold member 20a which cooperates or mates with acomplementary mold member 20b to mold the part. In the embodiment beingdescribed, the press 18 is a compression press like the 250 ton BipelPress, manufactured by Bipel of England, and the press controller 178may be a controller provided by Allen Bradley which may be coupled tocontroller 32.

The mold 18 also comprises the press heater 182 mentioned above which iscoupled to press controller 178 and which is capable of controlling thetemperature of the mold members 20a and 20b when they are molding thepart. In the embodiment being described, the mold heater 182 can varythe temperature of the mold members 20a and 20b from approximately 30°F. to 350° F. depending on the molding materials 14 being used. It is tobe noted that the press 18 is a compression press which includes apressure regulator 184 for regulating the pressure delivered to thebillet 16. In the embodiment being described, the pressure can vary from0 psi to 4000 psi. The press 18 also comprises a pressure gauge 186 andtimer 188 for displaying the pressure and mold time, respectively,during corresponding operation of the press 18.

The system 10 also comprises conveyance means or a conveyance system 190(FIG. 1). The function of the conveyance system 190 is to positionbillet 16 in mold member 20b after billet 16 is extruded from theextruding end 28b of barrel 28. In this regard, the conveyance system190 may be any suitable means for conveying the billet 16 directly intothe press 18, such as robotic arm, a hydraulic cylinder, a pneumaticcylinder, an electronic or mechanical conveyor or any other suitablemeans for causing billet 16 to be positioned in press 18. Furthermore,the conveyance system 190 may also comprise means for conveying orpositioning the plasticator 12 in operative relationship with the moldmember 20b such that when the billet 16 is extruded from barrel 28, itdrops directly onto mold member 20b. In this regard, the conveyancesystem 190 may comprise a wheel, shuttle and track arrangement (notshown) onto which the plasticator 12 may be positioned such that theplasticator 12 may be slidably moved towards and away from press 18. Forexample, the shuttle and track system would be coupled to controller 32so that when the press 18 moves to the open position shown in FIG. 1,the extruding end 28b of barrel 28 is moved into operative relationshipunderneath platform 180, such that when the billet 16 is extruded, itbecomes positioned on mold member 20b as shown in FIG. 1. Theplasticator 12 may then be moved or shuttled away from press 18 and theplatform 180 driven downward (as viewed in FIG. 1) to mold the part.After the part is molded, it may be removed from the press 18 and,during such removal, the plasticator 12 may again be shuttled or movedto extrude the next billet 16 onto mold member 20b. Other variations ofmoving the plasticator 12 may also be used. For example, the conveyancesystem 190 may cause the plasticator 12 to withdraw from press 18 slowlyso that the billet 16 is extruded substantially evenly over the lengthof the mold member 20b when the billet 16 is placed in the mold.

The molding materials 14 are preferably comprised of a polyester 192, acarbocylic or other carbocylics 194 and a preselected filler 196 (FIGS.1, 16a and 16b). In the embodiment being described, the polyester 192may include polyethylene terephthalate (PET), and the carbocylics 194may be an olefinic such as polycarbonate, polypropylene (PP),polyethylene (PE) or ethylene vinyl acetate (EVA).

The preselected reinforcement or filler 196 may comprise a reinforcingfiber, glass fiber, fly ash, clay, carbon or graphite fiber, shreddedreinforced fiber composite material, or like materials. It has beenfound that this apparatus and method can use fibers introduced toplasticator 12 with the other molding materials 14, without the fibersincurring significant damage. It should be appreciated, however, thatthis apparatus and system could be used with reinforced fibers, such asglass fibers, which range from the smallest available to as long as 6inches.

A compatibility enhancing agent or agents 198 may also be included asone of the molding materials 14 which is added into feed hopper 36. Itshould be appreciated that the polyesters 192, carbocylics 194,preselected fillers 196 and compatibility enhancing agents 198 may takeany suitable form which is capable of being received in the feed hopper24, such as the form of chips, pellets, flakes and fibers. In addition,reinforcing fiber may take the form of single strands, shavings, mats,edge trimmings or shreddings as may be contained in shredded or regroundreinforced composites containing such fibers in an existing polymermatrix. In other words, an existing thermoplastic polymer matrix havingone or more of the above molding materials 14 may be, for example,shredded and used.

The compatibility enhancing agent or agents 198 are heat activated andare chosen so as to enhance the compatibility of the thermoplasticpolymers, such as glass or glass fibers, and any other reinforcements orfillers which may be added. For example, olefinic polymers grafted withpolar functional moieties such as acrylic acid or maleic anhydride maybe mentioned. In this regard, the "Polybond" products available from BPChemicals are presently preferred for use.

Preliminary studies have indicated that "Polybond" product grades 1000,1001, 1002 and 1003 are suitable compatibility enhancing agents 198 thatmay be added to the thermoplastic polymers and fillers 196. Theseparticular "Polybond" products are polypropylene based coupling agentsgrafted with CA. 6% acrylic acid. The only difference between these 4grades of "Polybond" materials is in the melt flow rate "mfr". Theserange from 100 g/10 min. ("Polybond" 1000) to 12 g/10 min. ("Polybond"1003). The skilled artisan can choose the particular desired mfr basedupon the identity of the materials fed to the plasticator 12 and theinitial processing viscosity thereof desired. Other exemplarycompatibility enhancing agents 198 include "Polybond 1009 and 3009",both available from BP Chemicals. These polymers can be described ashaving high density polyethylene backbones grafted with either acrylicacid or maleic anhydride. The 1009 product is grafted with CA. 6%acrylic acid having a melt index of 6 g/10 min. while "Polybond" 3009 isgrafted with about 2% maleic anhydride and has a melt index of about 6g./10 min.

Other "Polybond" products can also be mentioned as being exemplary.These include the polypropylene based polymers grafted with varyingamounts of maleic anhydride. For example, "Polybond" 3001 is describedas a polypropylene polymer with grafted maleic anhydride branchespresent at a level of about less than 1/4%. This product exhibits a meltflow rate of about 5 g./10 min. "Polybond" 3002 is also exemplary and issimilar to the 3001 product except that its maleic anhydride content isabout twice as high and that it exhibits a MFR of 7 g./10 min.

Additionally, free radical generating polymerization catalysts such asperoxides may be admixed with ethylenically unsaturated acids oranhydrides and used herein as compatibility enhancing agents. Otherexemplary compatibility enhancing agents include the "EPOLENE" polymersavailable from Eastman Chemical and other experimental nucleating agentsalso available from Eastman and that are specifically formulated forpolyester rather than olefins. "EPOLENE" is a trademark of EastmanChemical.

The compatibility enhancing agent 198 which are normally fed to the feedhopper 36 in an amount of 1 to 10 (% by weight) based upon the weight ofthe thermoplastic polymeric material used.

An advantage of the system 10 is that it is capable of handling postconsumer molding materials or molding materials which have a relativelyhigh degree of contamination. For example, the molding materials 14 maybe commingled or contaminated polymeric material as typically found inthe post consumer waste stream. While the nature of contaminants and thepercent of occurrence varies from lot to lot as a natural feature ofwaste materials, they do, on average, typically contain similarmaterials and in similar quantities. For example, post consumerpolyesters (collected in the waste stream as PET) used in this processmay contain 90% PET, 5% HDPE, 2% PP, 0.5% EVA and the remaindercontaminants, including such things as miscellaneous paper and aluminumscrap.

The invention will now be described with reference to a number ofspecific examples which are to be regarded solely as illustrative andnot as restricting the scope of the invention.

EXAMPLE 1

First, molding materials were used without the compatibility enhancingagent 198. Sixty (60) parts of a mixed post consumer polymer batchcomprising PET, HDPE, PP and ethylene vinyl acetate (EVA) and 40 partsof scrap (landfill destined) glass fiber edge trimmings having nominal 2inch fiber lengths were charged to the single reciprocating screwplasticizer shown in FIG. 1. Compounding the billet 16 occurred in asingle thermodynamic cycle with a temperature rise to 430 degreesFahrenheit for a period of 30 seconds, at which time the resulting mixedand molten bulk molding billet 16 was delivered to the press where a6"×9" sample, 0.150 inch thick, was molded at a pressure of 3000 psi.The molded billet 16 was subjected to physical property tests and wasfound to exhibit a flexural strength of 10,300 psi, a flexural modulusof 700,000 psi and a notched IZOD of 0.43. These characteristics arerepresentative of a strong but brittle material considered to haveminimum desirability in product fabrication.

EXAMPLE 2

A mix of one-half post consumer polyethylene terephthalate (PET) derivedfrom soft drink bottles and one-half shredded scrap from a 40% glassreinforced polypropylene composite material resulting in short choppedglass lengths was charged to the plasticizer 12 shown in FIG. 1.Compounding in the barrel 8 occurred at 500 degrees Fahrenheit to 550degrees Fahrenheit for a time period of 60 seconds. The sample wastested and exhibited an average 12,500 psi flexural strength, a 435,000psi flexural modulus, and a notched IZOD of 5.7 ft.-lbs./inch. Thisrepresents a material with performance satisfactory for a wide range ofproduct uses.

EXAMPLE 3

Another example includes the use of the compatibility enhancing agent198. Sixty (60) parts of a mixed (commingled and contaminated) postconsumer polymer batch and 40 parts of scrap (landfill destined) glassfiber edge trimmings with nominal 2" fiber lengths were charged to theplasticizer 12 shown in FIG. 1. The polymer material was primarily PET,but also contained polycarbonate, HDPE, polypropylene, EVA andnon-polymer material such as scrap from aluminum cans and paper. Acompatibility enhancing agent 198 (Polybond 3009) was added to the mixin the plasticizer 12 at a ratio of 3% by weight based upon the weightof polymeric material fed. The first, second and third predeterminedtemperatures were set at 490 degrees Fahrenheit, 520 degrees Fahrenheit,530 degrees Fahrenheit, respectively, in the feeding plasticating area,and 540 degrees Fahrenheit in the delivery area. The knife head 96 wasset to 550 degrees Fahrenheit. The distance sensor was set a 110 mm. Theplasticizer 12 was operated with a screw speed of 20-40 rpm andcylinders 88 and 90 were set at 300 psi such that pressure of 50 psibuilding to 300 psi resulted in the reciprocating screw 42 being pushedby barrel back pressure to the 110 mm position. At this time (afterabout three total minutes from introduction of materials to theplasticizer 12), a mixed and molten billet 16 was then delivered to thepress 18 with mold faces 20a and 20b thereof heated to 80 degreesFahrenheit. A 6"×9" sample, 0.150 inch thick, was then molded at apressure of 3,000 psi. The sample was tested and exhibited a flexuralstrength of 20,310 psi, a flexural modulus of 980,000 and a notched IZODof 3.03 ft.-lbs./inch. This material would be suitable for a wide rangeof product applications having strength and modulus properties analogousto commercially available and widely used glass reinforced thermoplasticsheet materials.

A method and process for using system 10 and for creating in billet 16for molding a part will now be described. First, a post-consumerrecyclable plastic, such as PET, polypropylene, polyethylene andethylene vinyl acetate are collected as shown at step 200. If desired,these recyclable polymers may be separated (for example) by flotationseparation (as shown in block 202). The contaminated polyesters 192 andcarbocylics 194 along with the preselected reinforcements and fillers196 are loaded into feed hopper 36 (FIG. 1) of plasticator 12 as shownin block 204. As mentioned earlier herein, the compatibility enhancingagent 198 may also be added at this time, if desired.

It may be desirable to preheat the molding materials (block 206), inwhich case controller 32 energizes preheater 48 to preheat the moldingmaterials 14 (block 208) to approximately 100° to 350° F., depending onthe molding materials 14 selected. Controller 32 then energizes drivemotor 42 to rotatably drive agitator 40 to begin mixing the moldingmaterials 14 in feed hopper 36.

At block 210 a billet 16 is plasticized. Depending upon the part beingmolded, the predetermined characteristics of billet 16 are determined.Thus, the volume, density and length, for example, of billet 16 aredetermined. Once determined, the variable pressure regulator 117associated with cylinders 88 and 90 is adjusted to a pressure whichgenerally corresponds to the billet characteristics selected. Inaddition, one or more of the contact switches 140 of distance sensor 134are adjusted to correspond to the length and volume of the billet 16desired. In addition, the variable pressure regulator 117 associatedwith drive motor 92 is also adjusted so that drive motor 92 drives screw30 at an appropriate rpm. The controller 32 is also programmed with thefirst, second and third predetermined temperatures so that heatingcontroller 158 energizes the plurality of heaters 152, 154 and 156 toheat the feeding, blending and extruding portions 54, 56 and 58 to theappropriate temperature. For purposes of illustration only, it will beassumed that the pressure regulator 117 was set at 300 psi, the powersystem 96 pressure was set at 1000 psi, and the pressure regulatorassociated with drive motor 92 was set at 25 rpm, with contact switch140 being set at approximately 110 millimeters.

The molding materials 14 are then introduced to the feeding opening 46(FIG. 5). As best illustrated in FIGS. 4-10, controller 32 energizesdrive motor 92 of screw drive system 75 to rotatably drive screw 30 suchthat the molding materials 14 are gradually blended together into amixed molten suspension period.

The molding materials 14 are heated to approximately the firstpredetermined temperature when they are introduced between feedingportion 54 of barrel 28 and feeding section 60 of screw 30. Note that,due to depth 72 (FIG. 3) and pitch of the flights of the first pluralityof threads 66, the molding materials 14 start to become blended suchthat the reinforcing fibers, like glass fibers, are not damaged. Asscrew 30 rotates in the direction of arrow 31 in FIG. 5, the moldingmaterials 14 are forced from the feeding section 60 of screw 30 to theblending section 62 which is associated with blending portion 56 ofbarrel 28 when the screw 30 is in the home position shown in FIGS. 3 and4. Notice also that because of the taper of the core 30a of screw 30,the molding materials 14 become blended into a more homogeneoussuspension at the blending section 62 where the suspension is heated toapproximately the second predetermined temperature mentioned earlierherein. To further facilitate the mixing and blending of the moldingmaterials 14, the screw 30 may be provided with a blending section 62having a second plurality of threads 68 (FIG. 4) with a pitch which isgenerally smaller than the pitch of the first plurality of threads 66.Varying the number of threads per inch, pitch of threads and threaddepth facilitates accurately controlling the suspension and blendingtime of the molding materials 14, controlling the volume and density ofbillet 16, and controlling the velocity at which the molding materials14 are plasticated.

As the screw drive system 75 continues to drive screw 30 as mentionedabove, the mixed suspension is forced toward the storage area 124associated with the extruding portion 58 of barrel 28. In the storagearea 124, the molten suspension is collected, further blended and heatedto approximately the third predetermined temperature. The mixed moltensuspension ultimately engages the side 120a (FIG. 5) of knife 120 andbegins forming billet 16 as shown in FIG. 6. As the molten suspensioncontinues to collect in storage area 124, the pressure begins to build.

As the pressure approaches or exceeds 300 psi (i.e., the pressureapplied to cylinders 88 and 90) the biasing pressure of cylinders 88 and90 is overcome and the screw 30 begins withdrawing from passageway 52,thereby causing slidable block 78 to move in the direction of arrow 122(FIG. 1). As shown in FIGS. 6-8, the molten suspension begins buildingin the storage area 124. The slidable block 78 moves in the direction ofarrow 122 until contact switch 140 contacts switch 138 to generate thedistance signal which is received by controller 32. Controller 32 thenenergizes pressure valves 114 and 116 to stop drive motor 92. Controller32 also energizes pressure valve 110 to energize knife drive 118 tocause knife blade 120 to move from the closed position (FIGS. 8 and 14)to an open position (FIGS. 9 and 15). Controller 32 then energizespressure valves 108 and 110 to actuate cylinders 88 and 90 to pullslidable block 78 in a direction opposite arrow 122, thereby causing themolten suspension to be extruded through extruding opening 132 (FIGS. 9and 15). Controller 32 may then energize pressure valve 112 to actuateknife driver 118 to force knife blade 120 into the closed position,thereby separating the molten suspension to provide billet 16.

Although not shown, it should be appreciated that the controller 32 maycause the screw drive 75 and knife assembly 162 to provide a pluralityof billets 16 during a single stroke length of the cylinders 88 and 90.

The billet 16 may then be conveyed (block 212 in FIG. 16) to mold member20b in press 18 by the conveyance system 190 (FIG. 1). Other materials,such as sheet coating material or reinforcement material may beprepositioned (block 211) in the lower mold member 20b prior tointroducing billet 16 into the mold member 20b. Once located in thepress 18, controller 32 may energize press controller to, in turn,energize press driver 176 to drive platform 180 downward (as viewed inFIG. 1) to cause the part to be molded. In the example being described,the mold heater 182 heats the molding members 20a and 20b toapproximately 80 degrees Fahrenheit. In addition, the press 18 is set tocompress billet 16 at approximately 3000 psi with a controlled pressuregradient.

At block 214 (FIG. 16b), the part is then molded by press 18,

As shown in decision block 216, it may be desirable to perform a secondoperation on the part before it is removed from the press 18 or when thebillet 16 is molded. If such an operation is desired, it is conducted(block 218) and then the part is removed from the press 18 (block 220).In this regard, a second operation may comprise painting or otherwiseplacing a coating on the part, hot stamping a decal on the part,partially assembling the part, or molding or embossing a symbol on thepart. If a second operation is not performed on the part, the part isremoved from the press 18 at block 222.

Note that it may be desirable to integrally mold a surface texture orfinish to the part during the molding process. For example, a plasticsheet or film, such as the Teslin sheet, manufactured by PPG Industriesof Pittsburgh, Pa., may be integrally molded into the surface of thepart. For example, if the plastic sheet was selected, it would be cut tothe dimensions of the mold and placed in the mold prior to molding. Theside of the sheet which contacts the mold may be coated with an acrylicfinish to prevent the sheet from adhering to the mold during the moldingprocess. After the sheet is placed in the mold, the billet 16 can beplaced on the sheet and the part molded as described. If desired, asheet could be placed on both mold members 20a and 20b before billet 16is placed on mold member 20a. The billet 16 would then be placed on thesheet and molded as described above. This facilitates producing a parthaving a desired surface texture or finish on both sides. It is to benoted that, after the molding process, the polymer sheet is integralwith the part.

It should be appreciated that other types of materials may be integrallymolded into the part or into the surface of the part. For example, woodveneer sheets, burlap, or metal wire mesh may be molded into the part orinto the surface of the part.

Returning to block 224 in FIG. 16b, once the molding process iscompleted and the part is removed from the press, the process can berepeated for another part. At block 226, subsequent operations, such asadditional graphics, sheet material or printing, assembly, packaging andthe like may be performed on the part.

Advantageously, this invention provides a system and method for usingrelatively highly contaminated post-consumer polyesters and carbocylics(such as olefinics). The system and method also facilitates evenlymixing reinforced fibers having a length of 2.0 inches or more, withoutdamaging the fibers during the compounding, plasticating, extrusion andcompression molding process.

Such post-consumer scrap would normally require additional cleaning andseparation before use. This invention provides an apparatus and processfor using the contaminated post-consumer materials to produce a partwhich has physical, chemical and mechanical properties similar tonon-recycled materials.

Further, the method and apparatus provides a system for molding themolding materials 14 into a part using only a single thermal heat riseby controlling, coordinating and sequencing the temperature rise of themolding materials 14 as they go through the system 10. Using the singlethermal heat rise facilitates enhancing the molecular orientation of thepolymers which, in turn, causes the resultant part to have enhancedstrength characteristics when compared to other types of moldingprocesses. Also, a single heat rise facilitates reducing the materialdegradation that occurs to thermoplastic materials when they are heated.Further, because the pressures in the press 18 are adjustable, thesurface texture or finish or the resultant part can be controlled toenhance the aesthetic or functional appeal of the part.

The invention also provides a method and apparatus which is advantageousbecause it reduces or eliminates many of the intermediate handling andthermocycles from receipt of the post-consumer materials to the moldingof the part.

The described method and apparatus may utilize compatibility enhancingagent 198 which promote chemical bonding, for example, by increasing thepresence of hydroxyl groups and the reinforcing fibers while they aid inthe dispersion of reinforcement within the molten suspension.

Finally, molecular orientation within the billet 16 is enhanced bycontrolling the compression pressures and temperatures in press 18.

Advantageously, it should be appreciated that long fiber length can bemaintained by reducing the tortuous nature of the material path existingin many prior art devices and processes. This improvement of the pathresults from screw thread depths that allow fibers to move intact,allowing the screw to float on a film of molten material between itselfand the barrel. The lack of small orifices in delivering the materialthrough the plasticator 12 and the molding process allows formingwithout constraining the movement of fibers to form the part.

While the invention has been described with reference to certainspecific embodiments, this description is merely illustrative, and isnot to be construed as limiting the scope of the invention. Variousother modifications and changes may occur to those skilled in the artwithout departing from the spirit and scope of the invention as definedby the appended claims.

We claim:
 1. A method for creating a billet for molding a partcomprising the steps of:loading a barrel of a plasticator with aplurality of molding materials comprising a plurality of thermoplasticpolymers and long reinforcing fibers, said barrel having a screwrotatably mounted therein; heating said barrel; rotatably driving saidscrew to blend said plurality of molding materials together to create amolten suspension in a storage area of said barrel such that a majorityof said long reinforcing fibers remain intact; axially retracting saidscrew in a first direction as said molten suspension is accumulated insaid storage area; axially driving said screw in a second direction toforce said molten suspension out of said barrel, said second directionbeing opposite said first direction; and severing said molten suspensionto provide said billet.
 2. The method as recited in claim 1 wherein saidloading step further comprises the step of:loading said plasticator witha plurality of contaminated molding materials, said contaminated moldingmaterials being contaminated with one or more impurities.
 3. The methodas recited in claim 1 wherein said plasticator comprises a barrel; saidextruding step further comprising the steps of:sensing the approximatepressure applied to said molten suspension as it is created in saidstorage area; extruding said molten suspension out of said barrel aftersaid pressure reaches a desired pressure.
 4. The method as recited inclaim 1 wherein the heating step comprises the step of controlling thetemperature in the plasticator.
 5. The method as recited in claim 1wherein the barrel comprises a feeding end and an extruding end; a feedhopper associated with the feeding end and a knife associated with theextruding end;said method further comprising the step of: controllingthe temperature from the feed hopper to the knife so that the moldingmaterials loaded in the plasticator experience one temperature increase.6. The method as recited in claim 1 wherein said method furthercomprising the step ofcontrolling the pressure at which the screw drivesthe molten suspension to said storage area in the barrel.
 7. The methodas recited in claim 1 wherein said method further comprising the stepofcontrolling the pressure and speed at which the screw drives themolten suspension to said storage area in the barrel.
 8. The method asrecited in claim 6 wherein the plasticator comprises a slidable drivemotor coupled to the screw for axially and rotatably driving the screwto a home position where an end of said screw becomes associated with anextrusion end of said barrel,said controlling step comprising the stepof: biasing said screw in said home position with a desired amount ofpressure.
 9. The method as recited in claim 8 wherein said methodfurther comprises the step of:permitting the screw to withdraw from thebarrel when an actual pressure exceeds the desired amount of pressure.10. The method as recited in claim 9 whereby said driving step furthercomprises the steps of:stopping the rotation of said screw; axiallydriving the screw to force the billet out of an extrusion end of thebarrel.
 11. The method as recited in claim 1 whereinsaid screw comprisesa shaft having a first end associated with a feeder in the barrel and asecond end associated with an extruding end of the barrel; said shafthaving a pitch at said first end which is larger than a pitch of saidshaft at said second end.
 12. The method as recited in claim 1whereinsaid screw comprises a shaft having a first end associated with afeeder in the barrel and a second end associated with an extruding endof the barrel, said screw comprising a feeding section, a blendingsection and an extruding section, said screw having a greater number ofthreads at said blending section when compared to the number of threadsat said feeding section.
 13. The method as recited in claim 1 whereinsaid method further comprises the step of:preheating a plurality ofmolding materials to a desired temperature before they are loaded intothe plasticator.
 14. The method as recited in claim 1 wherein saidplasticator comprises a feed hopper having an agitator rotatably mountedtherein, said loading step further comprising the step of:loading saidfeed hopper with said molding materials; preheating said moldingmaterials to a desired temperature while they are in said feed hopper.15. The method as recited in claim 1 wherein said loading step furthercomprises the step of:loading a compatibility enhancing agent into saidplasticator.
 16. The method as recited in claim 1 wherein said barrelcomprises a feeding section, a blending section and an extrudingsection, said heating step further comprising the step of:heating saidfeeding section, said blending section and said extruding section toapproximately a first temperature, a second temperature and a thirdtemperature, respectively.
 17. The method as recited in claim 16 whereinsaid first, second and third temperatures are between approximately375-575 degrees Fahrenheit.
 18. The method as recited in 1 wherein saidplasticator comprises a barrel having a knife located at an extrudingopening at an end of the barrel, said knife being situated against saidend of said barrel to close said extruding opening, said method furthercomprising the steps of:actuating the knife to an open position;extruding said molten suspension through said extruding opening; drivingsaid knife to close said barrel and cut said molten suspension to formsaid billet to a desired shape.
 19. The method as recited in claim 1wherein said plasticator comprises a control system, said method furthercomprising:suspending said plurality of molding materials until saidbillet achieves desired billet characteristics in said plasticator. 20.The method as recited in claim 19 wherein said retracting step furthercomprising the steps of:sensing pressure in said barrel; retracting saidscrew in response to said sensed pressure.
 21. The method as recited inclaim 20 wherein said method further comprises the step of:using avariable pressure regulator in said plasticator to control pressureapplied to said molten suspension.
 22. The method as recited in claim 2wherein said impurities comprise either a polyolefin or a vinyl.